Analysis of adult S. mansoni secretory products after labeling in vitro with precursor sugars or amino acids reveals that worms incorporate and then excrete both large and small molecular weight products. The kinetics of excretion, amount of label retained, and the percent released into the media as large molecular weight material is characteristic of the precursor used. A neutral polysaccharide antigen has been isolated from S. mansoni eggs. This antigen differs from those previously described.